Example glass sealing methods for an oxygen sensor are set forth in U.S. Pat. No. 5,329,806, assigned to the assignee of this invention. In sensors such as in the '806 patent, the purpose of the glass seal is to isolate an end portion of an oxygen sensor from an air reference channel within the sensor. The seal prevents the gas being sensed, i.e., automotive exhaust gas, from leaking into and interfering with the air reference in the channel and the detrimental effect on the measurement output of the sensor that would result from such a leak.
In some prior attempts at achieving the glass seal, the glass seal has been implemented as both a structural and sealing element. Such seals have been prone to failures, including structural cracks allowing leakage into the air reference channel, failure of the glass to adhere to the outer housing of the sensor, and failure to maintain an effective seal over a wide operating temperature range such as required by an exhaust gas oxygen sensor.
Additionally, there is a chance that the sealing glass will see temperatures in excess of the glass transition temperature, in which case the region between the glass sensor and the shell of the sensor is in tension, impairing the structural integrity of the seal. Leaving the glass in tensile stress can lead to cracking in the seal, which allows infiltration of the sensed gas, i.e., automotive exhaust, into the air reference channel.